The present invention relates to a device for supplying a mixture of air and fuel to a manifold of an internal combustion engine of the type having a fuel atomisation and metering valve housed in a seat in a body of the device, which valve is electromagnetically operated and able to deliver a predetermined quantity of fuel to a region downstream of the valve.
Devices of this type normally include a pressure regulator arranged to regulate the pressure of the fuel in a region downstream of the valve. This regulator normally comprises a deformable diaphragm connected to a shutter member operable to control a fuel passage opening between the said upstream region and a discharge; the pressure regulator further includes a casing within which are defined two chambers for the fuel, which chambers are separated by the deformable diaphragm which is therefore in equilibrium between the pressures of the fuel which is found in the two chambers; one of these chambers is in hydraulic communication with the said region upstream of the valve while the other is in hydraulic communication with the region downstream of the valve.
Therefore, when the pressure upstream of the valve exceeds a predetermined value it causes a deformation of the diaphragm in a sense such as to displace the shutter member to increase the flow cross section of the said passage opening for discharging a certain quantity of fuel under pressure towards the discharge, thereby in this way reducing the pressure of the fuel in the said zone upstream of the valve.
Devices of the type indicated have various disadvantages.
First of all, they are constructionally very complicated because of the ducts which are necessary to connect the pressure regulator with the body of the device; in fact, the pressure regulator constitutes a completely separate unit from the body of the device and the said two chambers with which it is provided must be connected by means of suitable ducts to the regions upstream and downstream of the valve which are defined within the body of the device itself. These ducts are normally formed by means of small, suitably curved, tubes and by means of holes formed in the body of the device and in the casing of the pressure regulator. Consequently, a certain complexity in the constructional arrangement and a low reliability from the hydraulic point of view, is encountered both in the connection region between the small tubes and the first mentioned holes, and in the regions in which the said holes are closed by means of plugs of suitable type; in fact, the duct sections which are formed in the body of the device and in the casing of the pressure regulator usually comprise several holes in communication with one another, each of which is made as a through hole: only subsequently one end of these holes is closed by a suitable plug. It is evident that in the connection regions between the small tubes and the holes, and in the region in which these plugs are disposed, fuel pressure losses can easily be produced. Moreover, the ducts which are formed in the first indicated way, which are usually of a rather great length and have numerous and sharp variations in direction, also present a high resistance to the movement of the fuel; the pressure losses can be considerable and consequently the sensitivity of the pressure regulator and the rapidity of operation thereof is consequently reduced. Further, in known devices of the first indicated type, the first mentioned fuel ducts between the body of the device and the pressure regulator normally constitute an obstacle to the regular flow of air between the air intake opening of the device itself and the outlet for delivery of mixture to the manifold. In fact, the two said regions upstream and downstream of the attomisation and metering valve are normally located in the immediate proximity of the valve itself and this, in turn, is disposed within the air duct. Consequently, to put these regions in communication with the pressure regulator the first mentioned fuel ducts must traverse the said air duct thereby complicating the form of this and modifying the regular flow of air.